The invention relates to a continuous process for the preparation of permanently plasticized shaped articles of high strength, which comprise a chemically modified cellulose composition and possess a high swelling strength and a high mechanical strength as the result of the consolidation by means of crosslinking and are still adequately extensible due to their internal plasticizing.
Within the scope of the present invention, the term "shaped article" comprises fibers, strands, threads, tapes, and in particular, packaging material, such as, for example, films and especially tubings. In particular, the present invention relates to such a shaped article in the form of a tubing which further comprises in the wall thereof a reinforcement of fibrous material, in particular, a nonwoven fleece of paper fibers.
Shaped articles, manufactured by the process according to the present invention, in the form of tubing, especially fiber-reinforced tubing, are particularly suitable for use as an artificial sausage casing; artificial sausage casings of this type are not intended for human consumption.
It has been proposed to prepare crosslinked cellulose hydrate by a process wherein an aqueous liquid which contains a chemical crosslinking agent based on cyclic urea compounds containing at least two N-methylol groups and a secondary chemical plasticizer is allowed to act on shaped bodies of cellulose hydrate, which are in the gel state, and the shaped body is then subjected to an adequate heat treatment. Although the shaped articles which are manufactured by this known process possess a high mechanical strength and a high swelling strength due to the chemical crosslinking of the cellulose hydrate molecules, they are not permanently plasticized. The secondary chemical plasticizers can be extracted from the shaped article by means of a suitable solvent. Furthermore, this process has the disadvantage that "over-crosslinking" can readily occur in the shaped article and can cause an embrittlement of the material. This can take place because, depending on the length of time for which the material has been stored, a greater or lesser quantity of the introduced crosslinking agent reacts with the cellulose hydrate.